Electric toothbrushes generally have removable and exchangeable attachment brushes, so that a common handle can be used by multiple family members, each having his or her own personal attachment brush, or so that in case of wear of the attachment brush only this attachment brush, and not the electric toothbrush as a whole, need be replaced. In the process, various forces must be transmitted by the coupling between the attachment brush and the handle, including in particular the cleaning forces, drive forces, axial forces, and radial forces that act on the attachment brush, or that act on the handle in the form of reaction forces. The coupling of the attachment brush to the handle neck is generally achieved in such a way that the radial forces are absorbed or dissipated in the handle neck and the axial forces are absorbed or dissipated in the drive shaft. For this purpose, the tubular connecting piece of the attachment brush is generally pushed onto the neck of the toothbrush, and the drive shaft provided in the brush tube of the attachment brush is coupled to the drive shaft that protrudes from the end of the handle neck. An example of such a system is described in EP 0500537 B1, according to which the handle neck, and, in a correspondingly complementary fashion, the tubular connecting piece, are provided with a cross-section that deviates from a circular shape in order to enable radial forces to be better absorbed. In order to enable transmission of the axial forces, the drive shaft in the brush tube can be pushed onto the drive shaft on the handle and secured there by a latching connection.
For such an electric toothbrush, WO 00/76420 A1 proposes that the axial fixing and also the fixing against rotation be achieved at the handle neck. For this purpose, sawtooth-shaped rubber lips are provided in the tubular connecting piece of the attachment brush, which lips can be pushed onto the handle neck, the shape of which deviates from a circular shape. In addition, latching tongues are provided on the tubular connecting piece that can be pushed over the outer circumferential surface of the handle neck and can be latched there; this is intended to achieve additional securing against a pulling off in the axial direction. However, the additional axial securing achieved by this latching device is limited due to the outer circumference of the handle neck becoming dirty, for example with toothpaste residue and the like. In addition, the neck of the toothbrush is sometimes grasped with the fingers, which can cause unintentional disengagement due to external pressure on the latching connection.
Furthermore, U.S. Pat. No. 6,836,917 proposes an electric toothbrush that has an L-shaped groove on the neck of the toothbrush, into which a pin provided on the push-on connecting piece of the attachment brush moves, such that the attachment brush can be secured by pushing it on and rotating it, in the style of a bayonet coupling. In addition, provision is made for an engaging of the drive shafts. However, radial forces can cause unintentional disengagement of the bayonet coupling if these forces are applied in the correct (so to speak) direction of rotation relative to the handle, thus making additional securing measures necessary.
In addition, from DE 102 09 320 A1 an electric toothbrush is known in which only a toothbrush head can be exchangeably latched to the handle; i.e., the toothbrush head does not have a drive shaft for driving same. Instead, a drive shaft on the handle must be threaded into the toothbrush head, which can sometimes pose problems and requires a particular drive movement of the drive shaft.
Thus, there is a need for an improved electric toothbrush, an improved attachment part, and/or an improved handle for such an electric toothbrush, which avoid the disadvantages of the prior art and improve upon the latter in an advantageous manner. In particular, an easy-to-operate coupling should be created between the attachment part and the handle that reliably absorbs the arising axial and radial forces, holds the attachment part firmly and with as little play as possible on the handle, and nonetheless permits easy disengagement of the coupling.